I DraftPROCEEDINGS AND RECOMMENDATIONS FROM A CONFERENCE ON THE

APPLICATION OF GEOCHEMICAL MODELS TOHIGH-LEVEL NUCLEAR WASTE REPOSITORY ASSESSMENT

EDITORS

Gary K. JacobsEnvironmental Sciences Division

and

Susan K. WhatleyChemical Technolcgy Division

Manuscript Completed:Date of Issue:

December 1984

Prepared for theU.S. Nuclear Regulatory Commission

Office of Nuclear Materials Safety and SafeguardsWashington, D.C. 20555

under Interagency Agreement DOE 40-549-75

NRC FIN No. B0290

Prepared by theOAK RIDGE NATIONAL LABORATORYOak Ridge, Tennessee 37831

operated byMARTIN MARIETTA ENERGY SYSTEMS, INC.

for theU.S. DEPARTMENT OF ENERGY

under Contract No. DE-AC05-840R.21400

8501110338 541220PDR WKRES EXIORNLB-0290 PDR

ABSTRACT

A conference on the application of geochemical models to high-levelnuclear waste repository assessment was held to discuss the current sta-tus of geochemical code development, thermodynamic data bases, reactionkineti-cs, and coupled process models as applied to site characterizationand performance assessment activities. This proceedings Includesextended abstracts of the technical presentations given at the con-ference, a discussion of the role of geochemical modeling in predictingthe performance of repositories, and a set of recommendations whichidentify the key developments needed in order for geochemical models tobecome more applicable for quantitative evaluations of repositories.Detailed recommendations pertinent to the following subjects arediscussed: (1) improved simulation of repository performance throughinclusion of additional important geochemical processes and parametersInto current geochemical models, (2) more careful attention to uncer-tainties associated with geochemical model calculations, (3) assigningpriorities to (through sensitivity studies and critical evaluations) andthen improving and/or obtaining important thermodynamic data, and (4)addressing the importance of kinetics in simulating repository behavior.

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TABLE OF CONTENTS

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ABSTRCT . . .o . . . . . . . . .. . i . . a a a a a * a a a a * * * III

PREFACE * ... . .. ......... a * * * 9 m 9 e * 9 ix

ACKCNOWLEDGEMXENTS . . . . . . ,. . *. . . . * iv

1.0 INTRODUCTION . . .1.1 BACKGROUND . .1.2 PURPOSE . . .1.3 REFERENCES . .

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2.0 ROLE OF GEOCHEMICAL MODELS. . . . .2.1 APPLICATIONS OF GEOCHEMICAL MODELS

2.1.1 Sensitivity Studies . . . .2.1.2 Data Interpretations . . .2.1.3 Predictions of Performance

2.2 REFERENCES . . . . . . . . . . . .

3.0 RECOMMENDATIONS . . . . . . . . . . . .3.1 APPLICATIONS AND PROCESSES . . . .3.2 THEORY AND CODE DEVELOPMENT. . . . . .3.3 THERMODYNAMIC DATA . . . . . . . . . ,3.4 KINETICS AND COUPLED PROCESSES . . .3.5 GENERAL RECOMMENDATIONS. . . . . . . .3.6 REFERENCES . . . . .. . * . .. .

CONFERENCE PROCEEDINGS

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4.0 SOLUTION CHEMISTRY: THEORY, CODE DEVELOPMENT, ANDNON-REPOSITORY APPLICATIONS . . . . . . . . . . . . a a 0 . 0 S

Thermodynamic Problems in Speciatlon ModelingH. L. Barnes

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Prediction of Mineral Solubilities and Diagenesisin Rock/Water Association at High-Temperature . .

N. Killer, J. H. Weare, J. Greenberg

PHREEQE: Status and Applications . . . . . . . .L. N. Plummer and D. L. Parkhurst

MINTEQ Geochemical Reaction Code:Status and Applications . . . . . . . . . . . .

K. M. Krupka and J. R. Morrey

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EQ3/EQ6: Status and Applications . . . . . . . . . . . . a . .T. J. Wolery

5.0 THERMODYNAMIC DATA. . . . . . . . . . . . . . . . . . . a . . a

Complexes of Actinides with NaturallyOccurring Organic Compounds . . . . . . . . . . . . . . . . . .

G. R. Choppin

Experimental Determination of Stability Constants of theCarbonate Complexes of Uranium and Neptunium * . . . . . . . .

L. Maya

Temperature Dependence of ActinideSolubilities and SpeciatIon . . . . . . . . . . . . .

R. J. Silva

Neptunium and Technetium Behavior in Geologic SystemsR. E. Meyer, A. D. Kelmers, W. D. Arnold,J. S. Johnson, J. H. Kessler, R. J. Clark,C. C. Young, F. I. Case, and C. G. Weatmoreland

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Thermodynamic Properties of GeologicMaterials: Status and Future . . . a . . a . .

J. L. HaasC * * a 0 a a C

6.0 KINETICS AND COUPLED PROCESSES . . . . . . . . . . . . . . . .

Modeling Water/Rock Interactions . . . . . . . . . . . .P. Ortoleva

Coupled Geochemical and Solute TransportCode Development . . . . . a . . . . . . . . . . . . .

J. R. Morrey and C. Hostetler

Flow/Reaction Models of Natural Systems . * .a . . . . .C. H. Moore

Comparison of Dissolution versus PrecipitationKinetics in Silicates . . . . . . . . . . . . . . . . . . .

A. C. Lasaga

7.0 APPLICATIONS OF GEOCHEMICAL MODELS . . . . . . . . . . . .

CANADIAN PROGRAM:

Applications of Geochemical ModelingIn the Canadian Program . . . . . . . . . . . . . . . . . * . .

N. C. Garisto

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BASALT WASTE ISOLATION PROJECT:

Applications of Geochemical Modeling to High-Level NuclearWaste Disposal at the Hanford Site, Washington . . . . . . .

T. 0. Early, J. Myers, E. A. Jenne

NEVADA NUCLEAR WASTE STORAGE INVESTIGATIONS PROJECT:

Matrix Diffusion Coefficients for the NNWSIWaste Package Environment . . . . . . . . . .a. . . . . . . .

K. G. Eggert and M. A. Revelli

Applications of Geochemical Modeling to Site Characterizationand Radionuclide Transport in the NNWSI Project . . . . . .

J. F. Kerrisk

OFFICE OF NUCLEAR WASTE ISOLATION PROJECT:

Chemical Modeling of Nuclear Waste Repositories in theSalt Repository Project . . . . . . . . . . . . . . . . . . .

G. Jansen, G. E. Raines,J. F. Kircher, and N. Hubbard

Ion-Interaction Modeling of Deep Brines,Palo Duro Basin . . . . . . . . . . . . . . . . .. .a ..

D. Melchior and N. Hubbard

8.0 LIST OF PARTICIPANTS o * . o * . . . a & o a o o a . . .

PREFACE

It is expected that geochemical models (e.g., solubility/speciation, reac-

tion path, coupled reaction/transport, hydrothermal chemistry, etc.) will

be used to help demonstrate that high-level radioactive waste can be safely

isolated in deep geologic formations, and that such a repository can be

shown to meet or exceed all the technical criteria and performance objec-

tives set forth in current regulations. Therefore, a conference was spon-

sored by the Oak Ridge National Laboratory and the U.S. Nuclear Regulatory

Commissionl to discuss the application of these calculational methodo-

logies to the assessment of the safety and performance of repositories.

The purpose of the conference was to summarize and discuss the current sta-

tus of geochemical code development, thermodynamic data bases, reaction

kinetics, coupled process models, and the application of geochemical models

to high-level nuclear waste repository site characterization and perfor-

mance assessment activities. The goal of the conference was to develop a

consensus, to the extent possible, on the capabilities and limitations of

geochemical models. Specific technical recommendations related to geoche-

mical modeling resulted from the conference.

WAlthough sponsored by the U.S. Nuclear Regulatory Commission, theconference was intended to be a technical meeting and to provide a forumfor scientific discussions and recommendations which could then be utilizedby the U.S. Nuclear Regulatory Commission, U.S. Department of Energy, orany other interested agency, party, or individual. Therefore, the ideasexpressed in these proceedings are not necessarily endorsed by the U.S.Nuclear Regulatory Commission. The thoughts and facts presented in theextended abstracts of Chapters 4-7 are solely those of the authors.Statements contained within Chapters 1-3, although resulting fromdiscussions during the conference and reviewed by the chairpersons andspeakers, are the responsibility of the editors.

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4.

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The conference consisted of several sessions, each devoted to a particular

topic of importance to geochemical modeling. The sessions and

corresponaing chairpersons are listed below.

Session l:

Session II:

Session III:

Session IV:

Session V:

Solution Chemistry: Theory, Code Development, andNon-Repository Applications - H. Lo Barnes, ThePennsylvania State University

Thermodynamic Data - G. R. Choppin, Florida StateUniversity and R. J. Silva, Lawrence BerkeleyLaboratory

Kinetics and Coupled Processes - P. Ortoleva,Indiana University and Geochem Research Associates,Inc.

Applications of Geochemical Models - A. C. Lasaga,Yale University

Summary and Conclusions - G. K. Jacobs, Oak RidgeNational Laboratory

Chapter 1 introduces the problem of high-level nuclear waste Isolation and

provides a brief discussion of disposal concepts, regulations, and geochem-

ical models. Chapters 2 and 3 are the result of debate during the con-

ference, especially Session V, and are based on the presentation and

discussion of ideas related to two questions posed at the beginning of the

conference. The recommendations in these two chapters were prepared by the

editors, with the invaluable help of the chairpersons. The speakers

reviewed the recommendations to help ensure the views expressed during the

conference are fairly represented. Chapter 2 presents a discussion of the

role which geochemical models should play in evaluating the geochemical

processes Important to the performance of a HLW repository. Chapter 3 pre-

sents recommendations concerning the application and development of geochem-

ical models, thermodynamic data, and kinetics and coupled processes. In

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addition, Chapter 3 presents some general recommendations related to the

implementation of the technical recommendations.

Chapters 4 - 7 include extended abstracts summarizing material presented

by the authors during the conference. The purpose of Session I (Chapter

4) was to discuss currently available geochemical codes and some theoreti-

cal aspects of thermodynamic calculations. The codes PHREEQE, MINTEQ, and

EQ3/EQ6 were chosen for detailed discussion because these codes are pres-

ently the most widely used for high-level waste applications within the

projects of the Department of Energy. Session II (Chapter 5) emphasized

the state of thermodynamic data bases used to support geochemical calcula-

tions. Session III (Chapter 6) addressed the Increasingly Important con-

sideration of coupling thermodynamics, fluid flow, reaction kinetics, etc.

in order to more appropriately model the geochemical processes important to

repository systems. Session IV (Chapter 7) provided the opportunity for

Individuals from repository projects of the United States and Canada to

give examples of - and plans for - the use of geochemical models in charac-

terizing the geology, geochemistry, and hydrology of candidate repository

sites, evaluating geochemical processes within the repository system, and

assessing the potential performance of the disposal system.

We hope that the reader finds these proceedings a useful overview of the

role geochemical modeling could play in evaluating the safety and perfor-

mance of high-level radioactive waste repositories. It is hoped that the

recommendations are not simply discarded as a "wish list," but rather, are

given due consideration, because we feel that the disposal of nuclear waste

should not be regarded lightly and that it deserves being addressed through

xii

proper scientific and engineering approaches. The complexity of technical

problems involved in waste disposal Is great, the potential for inadvertent

errors high, and the repercussions from such errors not entirely known at

this time. Therefore, care should be taken to not overlook or avoid tough

technical questions just because data is not available, time is short, or

someone "doesn't think Its a problem." In attempting to achieve the safe

disposal and isolation of nuclear waste, 'no surprise is the best

surprise."

Gary K. JacobsSusan K. Whatley

. t

ACKNOWLEDGEMENTS

We would like to express our thanks to the chairpersons H. L. Barnes,

G. R. Choppin, A. C. Lasaga, P. Ortoleva, and R. J. Silva, who helped

run the conference and pull together the recommendations resulting from

the discussions during the week. We thank the speakers who graciously

took the time to present information at the conference and prepare writ-

ten summaries for the proceedings. Special thanks go to L. N. Plummer

and J. L. Haas of the U.S. Geological Survey who, though not able to

attend the conference, nevertheless kindly prepared written papers. The

chairpersons, speakers, and participants are thanked for their contribu-

tions to the conference through stimulating discussion and debate -

without this, the conference would have been of little consequence. The

chairpersons and speakers provided reviews of the proceedings to help

ensure that the recommendations are consistent and fair in presenting

views expressed during the conference, however, the editors assume full

responsibility for the final version. K. J. Kitts, A. R. Calhoun, and

B. S. Reesor were Indispensable in helping with organizational details

of the conference. K. J. Kitts patiently helped with the preparation of

the proceedings and C. H. Shappert provided editorial assistance.

xiv

1.0 INTRODUCTION

1.1 BACKGROUND

The disposal of high-level radioactive waste is a complex issue

involving science, engineering, economics, and sociology. Whether or

not one supports the continued development of nuclear power and/or the

proliferation of nuclear weapons, the waste products from past activi-

ties are with us now and must be properly Isolated from the environment

in order to protect the health and welfare of the human population as

well as natural habitats. The option of 'no action" is clearly not

acceptable because the temporary storage techniques currently in use are

not feasible for continued long-term containment and isolation. More

sophisticated surface storage techniques could be developed which would

be feasible for time periods of 50 to 100 years. Thus, the current

situation is not so desperate that an accelerated program designed to

meet arbitrary deadlines is the only solution. It is an unavoidable

fact that A poor decision now could be regrettable for thousands of

years. Therefore, the Information base necessary to properly evaluate

and predict the safety and performance of a high-level nuclear waste

repository should be developed by addressing tough technical and social

problems in a rational manner and not overlooking Issues of unproven or

unknown impact simply because data may not exist or may be difficult to

obtain.

The current concept for the disposal of high-level radioactive waste

(HLW) In the United States is that of containment and isolation in deep

geologic formations utilizing a combination of natural and man-made

barriers. A typical repository system may include a waste form con-

tained within one or more metallic or ceramic canisters, packing

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material (crushed rock, clay, etc.) around the canister, and backfill

(crushed rock) and seal materials (cement, compacted clay, etc.) to fill

and seal of f the rooms and shafts created during the construction and

operation of the repository. These engineered barriers are placed

within a geologic setting which may possess several barriers itself

(e.g., location above deep water table, impermeable rock layers,

favorable geochemistry for precipitation and/or sorption of radionucli-

des, slow groundwater velocities, etc.). The concept of a deep geologic

repository, and some of its variations, has been previously described

(e.g., 1, 2, 3, 4, 5) and the reader is referred to these articles for

additional details.

The philosophy of the multiple barrier approach is to have a system com-

posed of several barriers, each significantly contributing to the

overall performance of the repository in an independent mamner. In this

day, the likelihood of a catastrophic failure will be reduced, because

if one barrier fails, others of a different type could still function to

some degree. In addition, because of the long time periods (thousands

of years) required to reduce the hazards from HLW to an acceptable

level, predictions of performance will be somewhat uncertain.

Therefore, utilizing several different barriers can provide for added

confidence in the performance of the system. Examples of ways in which

the performance of natural geologic barriers and engineered components

can be combined to achieve a desirable allocation of performance are

discussed by Deju et al. (6) and Smith et al. (7).

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3

Ultimately, the goal of a repository must be to limit the rate, con-

centration, and accumulation of radionuclides released to the accessible

environment to an acceptable level, because absolute containment for

thousands of years cannot be guaranteed. Though many complex lnterac-

tions are involved, hydrologic and geochemical processes will generally

control the timing, rate, and quantity of radionuclides released from a

repository. Bird and Fyfe (2) describe some of the geologic con-

siderations involved In assessing the behavior of a repository system.

Geochemical considerations will be important in the selection of

materials for waste forms, canisters, packing, and backfill, as well as

In the selection of a site for a repository. Confident predictions of

the long-term performance of a repository, involving the corrosion of

canisters, the dissolution of waste forms, and the subsequent interac-

tions of the radionuclide-contaminated groundwater with engineered

materials and host rocks, will require a significant understanding of

geochemical processes and conditions in this system.

The National Waste Policy Act of 1982 (Public Law 97-425) specifies that

the U.S. Departmunt of Energy (DOE), the U.S. Nuclear Regulatory

Commission (NRC), and the U.S. Environmental Protection Agency (EPA) are

responsible for conducting the activities necessary to implement the

siting, construction, and eventual operation of a HLW repository in the

United States by the year 1998. The EPA has established a set of draft

environmental standards (8) which define limits for the cumulative

release of radionuclides to the accessible environment for a period of

10,000 years. The NRC is responsible for ensuring that the EPA stan-

dards are met. To help provide confidence that a repository system will

4

meet the EPA standards, the NRC has established additional performance

objectives for a HLW repository (9). These objectives are (for precise

wording and definition of terms, see 9): (1) substantial containment of

radionuclides within the waste packages for a period of time no less

than 300 to 1,000 years, (2) a rate of release of radionuclides from the

engineered barrier system no greater than lo- per year of the inven-

tory calculated to be present at 1,000 years, and (3) a pre-waste-

emplacement groundwater travel time from the disturbed zone around a

repository to the accessible environment of at least 1,000 years. The

DOE has the responsibility to develop the information and technology

necessary to site, license, construct, and operate the repository. The

current schedule in the National Waste Policy Act requires that most of

the research and development be completed by approximately 1988 so that

an application for a license can be submitted to the NRC. Complete

information may not be required at this time because the initial

authorization will only be to begin construction of a repository;

another authorization from the NRC will be required to begin actual

operation of the repository and emplacement of waste.

In order to focus on more specific technical items related to the per-

for-lance objectives listed above, the NRC has developed a set of

'idsues' which, when resolved, will help ensure that the performance

objectives are met and that a repository can be licensed. Three geochem-

ical issues have been identified which relate to the nature of geochem-

ical processes and conditions in and around the repository during three

periods of repository history:

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1. What are the present geochemical conditions?

2. What are the changes in the geochemical conditions/processes as a

result of waste emplacement?

3. What are the future geochemIcal processes/conditions that will

affect release and transport of radionuclides to the accessible

environment?

Because geochemical processes within the geologic setting can represent

a significant barrier to the release of radionuclides, it is desirable

to establish an understanding of geochemical conditions prior to,

during, and after waste emplacement. This knowledge will enable the

effects of repository construction, operation, and waste emplacement on

the geochemical conditions and processes of the geologic setting to be

evaluated. Thus, an assessment can be made of the containment, release,

and transport of radionuclides from the waste packages through the

disturbed zone to the accessible environment.

Geochemical models can be used to Interpret and predict chemical rela-

tionships in geologic systems and, therefore, may be of substantial use

in analyzing the geochemical processes Important to the performance of

HLW repositories. There are many types of geochemical models available

with the ability to calculate some or all of the following: (1) aqueouis

speclation, (2) saturation indices, (3) mass transfer, (4) reaction

paths, (5) sorption reactions, (6) reaction kinetics, and (7) ground-

water flow coupled with one or more of the above geochemical processes.

Specific geochemical models have individual capabilities which make them

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6

useful for one application or another. For a brief review of geochemi-

cal models and some of their applications and limitations, see Jenne

(10, 11).

The term "geochemical model' has been generally adopted for computer

codes which perform calculations such as those listed above. However,

"geochemical model" is a somewhat misleading term. A geochemical model

is really made up of three parts: (1) a model, (2) a computer code, and

(3) a data base. The model represents the physical, chemical, geologi-

cal, thermodynamic, and kinetic concepts (and their mathematical

representations), which provide the basis for the calculations. The

computer code consists of the algorithms necessary to obtain quan-

titative solutions to the model. The data base for a geochemical model

can include several types of data depending on the nature of the model.

Data bases can include: fundamental thermodynamic properties, kinetic

rate law expressions and constants, empirical relationships, chemical

information about the system of interest, hydrologic parameters, etc.

Because the term "geochemical model" Is currently in wide use, and by

precedent refers to calculations utilizing the three components

discussed above (i.e., model, code, and data base), 'geochemIcal model"

will continue to be used throughout these proceedings to refer to any

calculational methodology involved in the simulation of physical and

chemical processes important to the evaluation .f a geologic system.

1.2 PURPOSE

It is sometimes stated that the disposal of HLW Is not a technical

problem, but rather a soclo-politlcal issue, and that adequate tech-

nology to dispose of the waste currently exists. There Is no question

7

that the technology exists to manufacture waste packages and to emplace

them in deep geologic formations. However, the more pressing Issue is

whether the information and technology exist to predict, with reasonable

assurance, that the emplaced waste, once disposed of, will continue to

be contained and isolated to an acceptable level after operation of the

repository is completed. The National Academy of Sciences (1) has

concluded that current technology is sufficient to proceed with the

program of geologic repositories for HLW, but that, even though It is

likely a geologic repository for RLl will be successful, final decisions

must await at-depth characterization and testing of actual sites.

Prediction of the behavior of a complex system of geologic and engi-

neered materials for 10,000 years is unprecedented. In the past few

years there has been some progress in addressing some of the geochemical

processes important to the long-term performance of RLW repositories.

However, it is not entirely clear that the current schedule in the U.S.

will continue to successfully provide all the necessary Information in a

timely manner. It is Intended that the recommendations from this con-

ference be used to help elucidate mome key items related to geochemistry

which may require more careful consideration than has been given in the

past.

The focus of the conference was confined to the application of geochemi-

cal models to HLW repository assessments. Therefore, the scope of the

resulting recommendations is purposely limited. As will be obvious,

there are significant areas of research and development (e.g., tec-

tonics, hydrology, meteorology, climatology, metallurgy. etc.) important

8

to HLW isolation which are not addressed. The omission of these sub-

jects is regrettable but, hopefully, other detailed conferences can be

held which can better accommodate these topics. No attempt was made to

assign priorities to the recommendations, as this was beyond the scope

of the conference. A discussion of general recommendations related to

the management and funding of the technical recommendations is Included

because, within the directives of rhe current programs in the United

States, there appears to be little support of the type of studies

required. It is the position of the editors and chairpersons of the

conference that unless some of the more important recommendations con-

tained herein are Implemented, it Is unlikely that the safety and per-

formance of a repository can be established to an appropriate level of

confidence.

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1.3 REFERENCES

1. NAS, A Study of the Isolation System for the Geologic Disposal ofRadioactive Waste, Waste Isolation Systems Panel, T.H. Pigford,chairman, National Academy of Sciences/National Research Council,Washington, D.C. (1983).

2. G. W. Bird and W. S. Fyfe, 'The Nuclear Waite Disposal Problem - AnOverview from a Geological and Geochemical Perspective", ChemicalGeology, 36, 1-13 (1982).

3. J. D. Bredehoft and T. Maini, "Strategy for Radioactive WasteDisposal in Crystalline Rocks", Science, 213, 293-296 (1981).

4. 1. J. Winograd, "Radioactive Waste Disposal in Thick UnsaturatedZones', Science, 212, 1457-1464 (1981).

5. B. L. Cohen, 'The Disposal of Radioactive Wastes from FissionReactors", Scientific American, 236, 21-31 (1977).

6. R. A. Deju, H. Babad, G. K. Jacobs, and H. S. Sunsky, 'PerformanceAllocation Traceable to Regulatory Criteria as Applied to SiteCharacterization Work at the Basalt Waste Isolation Project",Waste Management '83, I_, 135-141 (1983).

7. M. J. Smith, M. S. Bensky, and T. B. McCall, "Progress in theDevelopment of Waste Package Performance Requirements for aRepository Located in Basalt", Waste Management '83, I,143-148 (1983).

8. EPA, Environmental Standards and Federal Radiation ProtectionGuidance for Management mnd Disposal of Spent Nuclear Fuel, High-Level, and Transuranic Radioactive Wastes, 40 CFR, Part 191,U.S. Environmental Protection Agency, Washington, D.C. (1983).

9. NRC, Disposal of High-Level Radioactive Wastes in GeologicRepositories: Technical Criteria, 10 CFR, Part 60, U.S. NuclearRegulatory Commission, Washington, D.C. (1983).

10. E. A. Jenne, Chemical Modeling in Aqueous Systems, E.A. Jenne,ed., American Chemical Society Symposium Series 93, Washington,D.C. (1980).

11. E. A. Jenne, Geochemical Modeling: A Review, PNL-3574, PacificNorthwest Laboratory, Richland, Washington (1981).

S2.0 ROLE OF GEOCHEMICAL MODELS

What role should geochemical modeling play in characterizing andunderstanding the nature and performance of high-level radioactive wasterepositories?

There was a general consensus at the conference that modeling the

geochemical behavior of a HLW repository is an essential part of esti-

mating the overall safety and performance of the system as a function of

time. This conclusion resulted from the recognition that there is no

viable alternative to numerical simulation of geochemical processes

important to repository performance. It is not possible 3 adequately

assess the geochemical behavior of a repository system through labora-

tory and/or field techniques alone. In attempting to scale down mass

transport processes important to a repository, there is an unavoidable

loss of similitude between a system of geologic proportions in space and

time, and short-term laboratory, bench, or field tests. Parameters such

as porosity, permeability, grain size, thermal conductivity, and,

perhaps most importantly, time, are not always amenable to changes in

scale which would allow processes to be accelerated such that meaningful

results can be obtained within a reasonable period of time (e.g., weeks

to months). Therefore, numerical simulation of geochemical and mass

transport processes, in conjunction with careful experimental and field

observations, is probably the only means available to estimate the

geochemical behavior of a repository system for time periods of

thousands of years.

In the preceding paragraph the phrase "to estimate" was used rather than

'to establish." This distinction is Important because uncertainties

10

will always be present in assessing geochemical processes Important to a

repository. One will never absolutely establish all facets of geochemi-

cal behavior. Rather, one will be forced to accept a philosophy of

trying to achieve a 'best-guess" estimate which can be shown to be

reasonable and not overly optimistic. The oft-cited philosophy of using

"conservative" estimates does not necessarily relax requirements on the

amount and/or quality of information necessary to describe the geoche-

mistry, because establishing conservatism presumes a certain level of

understanding of the processes and mechanisms involved. Otherwise, one

would not know whether a value is conservative or not.

What really is involved in the modeling of geochemical processes impor-

tant to the performance of a HLW repository Is an extrapolation from

small-scale, short-term laboratory and field tests to full-scale, long-

term geologic behavior. It Is well-established that any extrapolation

outside the limits of existing data can be unpredictable and uncertain,

as well as completely meaningless In physical terms, unless the method

of extrapolation Is fundamentally sound. Acceptable extrapolations

involve establishing a theoretical framework for the parameter or pro-

cess of interest and obtaining enough data so that the fundamentals of

the concept can be validated. For example, an arbitrary five-term poly-

nomlal can provide an excellent fit to high-temperature (>298 K) heat

capacity data, thereby retaining the accuracy and precision of calori-

metric methods in the equation (I and 2). However, using this equation

beyond available heat capacity data can result in extrapolations which

violate fundamental thermodynamic principles. Therefore, a more

appropriate approach might be to use the five-term polync~uial only

S

12

within the region where data exists, and to use an equation which can be

constrained to obey thermodynamic precepts governing the behavior of

heat capacity as a function of temperature (3) for extrapolations beyond

the limit of existing data (4). In a similar manner, geochemical pro-

cesses and parameters Important to a HLW repository need to be described

by fundamental concepts appropriate for reproducing data as well as for

making physically meaningful extrapolations constrained by some esti-

mated amount of uncertainty.

There are many examples in the geologic literature of studies which have

successfully combined fundamental data and modeling calculations to eva-

luate the behavior of natural systems (e.g.. 5, 6, 7, 8, 9, and 10).

Though all parameters and mechanisms are not always explicitly

established, significant Information can be obtained through careful

data collection, experimentation, theoretical calculations, and com-

parison to natural systems. An obvious difference between most geologic

studies such as these and the problem of HLW isolation is that there is

no repository in existence today which model predictions can be tested

against. Therefore, pure prediction, as opposed to interpretation and

comparison, will be required for repository simulations. Because of the

necessary reliance on predictions and long-term extrapolations, one can-

not stress strongly enough the importance of establishing sound concep-

tual models and theoretical frameworks for the evaluation of geochemical

processes important to HLW repositories.

2.1 APPLICATIONS OF GEOCHEMICAL MODELS

Geochemical models can be useful in addressing each of the three issues

listed previously in the Introduction. For example, geochemical models

13

can aid in elucidating the nature of, and possible controls on, the

geochemical conditions In the undisturbed geologic setting. Parameters

and characteristics which can be Included in such evaluations include:

temperature, pressure, groundwater chemistry, pH, redox potential,

mineralogy of the host rocks, etc. Examples of such studies (not

limited to waste isolation) include: (7), (11), (12), (13), (14), (15),

(16), (17), (18), and (19).

Emplacement of HLW into a geologic repository can substantially affect

the pre-emplacement geochemical conditions. Therefore, the use of

gecchemical models to help evaluate these potential changes seems

imperative because a comprehensive set of experiments is not possible.

Important considerations include: (l) physicochemical interactions bet-

ween heated groundwaters, host rocks, and engineered materials, (2)

radiation damage to solids, (3) radiolysis of groundwaters, and (4)

residual effects of repository construction (e.g., introduction of air,

bacteria, organic material, etc.). Studies in this area are not abun-

dant, as much of the work is just underway. Wolery and Delaney (20)

have modeled high-temperature (90 - 150'C) water-rock interactions

pertinent to the candidate repository site at the Nevada Test Site.

Neretnieks (21) has addressed the possible movement of a redox front

as a result of migrating H202 formed via alpharadiolysis. Modeling of

rock-water systems at elevated temperatures is common within the geolo-

gic literature and the interested reader is referred to (5), (22), (23),

(24), and (25, and references therein).

14

The eventual release and transport of radionuclides Is also amenable to

geochemical modeling calculations, provided that the necessary sup-

porting data is available. Consideration needs to be given to the

alteration (corrosion) of engineered materials (packing, backfill,

metals, etc.) and the mobility of radionuclides during and after the

time period of release of radionuclides from the failed waste packages.

Simulations of processes such as these have been rather simplistic to

date and have mostly concentrated on calculating possible solubility

controls for radionuclides (e.g., 26, 27, 28, 29, and 30), although

Wolery (31) has modeled the coupled dissolution of spent fuel and copper

canisters. Calculations such as these serve to Illustrate the utility

of geochemical models, although the validity of the conceptual model of

equilibrium, rather than kinetic, processes controlling the con-

centration of radionuclides In a repository has yet to be established.

2.1.1 Sensitivity Studies

Geochemical models, when operated in a sensitivity mode, can be used to

help identify deficiencies in conceptual models, data, and analytical

techniques. For example, the impact of uncertainties in the stability

constants for aqueous complexes of radionuclides on the solubility of a

radionuclide-bearing phase can be investigated (32). This is not to

say, however, that sensitivity studies can replace scoping experiments.

It is important to recognize that all important complexes must at least

have estimated data available for a sensitivity study to have any

meaning at all. Sensitivity studies can also be used to help identify

areas of Improvement for site characterization activities. For example,

15

if low concentrations of some complexing agent can significantly

increase the solubility of some radionuclide-bearing phase, then

research into improved detection limits, precision, and accuracy of

analytical techniques for measuring the presence of this chemical

constituent would be warranted (32). Early et al. (33) discuss how

modeling studies aid in identifying solid phases which could require

special attention during the characterization of host rocks, because

they are calculated to be possible solubility controls for the ground-

water and could be important for the sorption of radionuclides. In the

area of kinetics, the importance of relative rates of dissolution, pre-

cipitation, sorption, etc. can be evaluated and used to help establish

priorities for detailed experimentation. Sensitivity studies can also

be used to evaluate alternative conceptual models and, thus, avoid

problems which stem from preconceived notions about the behavior and

performance of a repository system. For example, Ortoleva (34) has

pointed out that potential chemical instabilities (which are found in

laboratory experiments and natural occurrences) may be inadvertently

missed if sensitivity studies utilizing coupled chemical

reaction/transport models are not performed.

2.1.2 Data Interpretations

Currently, this is probably the most widely used application cf geochem-

ical models. Models can be used to help establish a qualitative

understanding of mechanisms and to develop guidelines for future direc-

tions of work In topics including: field tests, corrosion tests,

waste/barrier/rock/water interactions, conceptual groundwater flow

models, waste form dissolution, etc. For example, models can be used to

16

evaluate the relative saturation state of groundwaters with respect to

phases present in the host rocks (e.g., 7). This type of information

can be used to help assess the validity of conceptual groundwater flow

models by comparing the chemical trends and likely flow directions. In

addition, analyses such as this can be of help in evaluating the Impor-

tance of kinetic effects in the evolution of the groundwater system, an

important factor when attempting to assess the impact waste emplacement

(i.e., elevated temperature - thus, accelerated kinetic processes) will

have on the ambient characteristics. One application of geochemical

models to the Interpretation of hydrothermal experiments is the deter-

mination of whether a final phase assemblage Is stable or metastable

(33), an important consideration If test results are to be used for

extrapolations. Grambow and Strachan (35) present an example of the use

of PHREEQE (36) to help interpret waste form dissolution tests.

2.1.3 Pred; ions of Performance

As discussed earlier, numerical simulation of geochemical processes is

the only rational approach for predicting long-term performance.

Unfortunately, the processes and parameters to be considered are

numerous and make the problem complex. Currently, there is no single

model available which can be used for such predictions. A complete

model consisting of a conceptual framework and necessary supporting data

is simply not available. However, there is presently a significant

amount of effort being expended in model development. The next chapter

contains recommendations relevant to model development and data collec-

tion. These recommendations are intended to complement the current on-

going activities and, if Implemented, result in a comprehensive model

17

which can be used to reliably estimate geochemical and mass transport

characteristics important to the performance of a repository.

, ~~~~~~~~~~18

2.2 REFERENCES

1. J. L. Hass, Jr. and J. R. Fisher, 'Simultaneous Evaluation andCorrelation of Thermodynamic Data," American Journal of Sclence,276, 525-545 (1976).

2. K. M. Krupka, R. A. Robie, and B. S. Hemingway, 'High-TemperatureHeat Capacities of Corundum, Periclase, Anorthite, CaA12Si 2 O8glass, Muscovite, Pyrophyllite, KAlSi 3 08 glass, Grossular, andNaAlSi308 glass," American Mineralogist, 64, 86-101 (1979).

3. K. Denbigh, 'The Principles of Chemical Equilibrium," CambridgeUniversity Press, New York (1971).

4. G. K. Jacobs, D. M. Kerrick, and K. M. Krupka, "The High-Temperature Heat Capacity of Natural Calcite (CaCO 3 )," Physicsand Chemistry of Minerals, 7, 55-59 (1981).

5. D. K. Bird, P. Schiffman, W. A. Elders, A. E. Williams, and S. 0.McDowell, "Calc-Silicate Mineralization in Active GeothermalSystems," Economic Geology, 79, 671-695 (1984).

6. S. L. Brantley, D. A. Crerar, N. E. Moller, and J. H. Wear^,"Geochemistry of a Modern Marine Evaporite: Bocana De Virrila,Peru," Journal of Sedimentary Petrology, 54, 447-462 (1984).

7. W. J. Deutsch, E. A. Jenne, and K. M. Krupka, 'SolubilityEquilibria in Basalt Aquifers: The Columbia Plateau, EasternWashington, USA," Chemical Geology, 36, 15-34 (1982).

8. W. E. Seyfried, Jr. and W. E. Dibble. Jr., "Seawater-PeridotiteInteraction at 300'C and 500 bars: Implications for the Origin ofOceanic Serpentinites," Geochimica et Cosmochimica Acta, 44,309-321 (1980).

9. J. J. Hemley, J. W. Montoya, C. L. Christ, and P. B. Hostetler,"Mineral Equilibria In the MgO-SiO2 -H 2 0 System: I. Talc-Chrysotile-Forsterite-Brucite Stability Relations," AmericanJournal of Science, 277, 322-351 (1977).

10. J. J. Hemley, J. W. Montoya, D. R. Shaw, and R. W. Luce, "MineralEquilibria in the MgO-Si0 2 -H20 System: II. Talc-Antigorite-Forsterite-Anthophyllite-Enstatite Stability Relations and SomeGeologic Implications in the System," American Journal ofScience, 277, 353-383 (1977).

11. R. D. Lindberg and D. D. Runnells, "Ground Water Redox Reactions: AnAnalysis of Equilibrium State Applied to Eh Measurements andGeochemical Modeling," Science, 225, 925-927 (1984).

a 19

12. P. A. Arditto, -Mineral-Groundwater Interactions and the Formationof Authigenic Kaolinite within the Southeastern Intake Beds of theGreat Australian (Artesian) Basin, New South Wales, Australia,"Sedimentary Geology, 35, 249-261 (1983).

13. W. Back, B. B. Hanshaw, L. N. Plummer, P. H. Rahn, C. T. RIghtmire,and M. Rubin, "Process and Rate of Dedolomitization: Mass Transferand 14C Dating in a Regional Carbonate Aquifer," Geological Societyof America Bulletin, 94, 1415-1429 (1983).

14. J. F. Kerrisk, Reaction-Path Calculations of Groundwater Chemistryand Mineral Formation at Rainier Mesa, Nevada, LA-9912-MS, LosAlamos National Laboratory, Los Alamos, New Mexico (1983).

15. L. N. PLummer, D. L. Parkhurst, and D. C. Thorstenson, "Developmentof Reaction Models for Ground-Water Systems," Geochimica etCosmochimica Acta, 47, 665-686 (1983).

16. W. M. Edmunds, A. Ho Bath, and D. L. Miles, "HydrochetdcalEvolution of the East Midlands Triassic Sandstone Aquifer,England," Geochimica et CosmochimIca Acta, 46, 2069-2081 (1982).

17. H. C. Claassen, "Estimation of Calcium Sulfate Solution Rate andEffective Aquifer Surface Area in a Ground-Water System nearCarlsbad, New flexico," Ground Water, 19, 287-297 (1981).

18. A. F. Wsaste, H. C. Claasien, and L. V. Benson, The Effect ofDissolution of Volcanic Glass on the Water Chemistry in aTuffaceous Aquifer, Rainier Mesa, Nevada, U.S. GeologicalSurvey Water-Supply Paper 1535-Q, U.S. Geological Survey,Washington, D.C. (1980).

19. F. W. Schwartz, 'The Origin of Chemical Variations in Groundwatersfrom a Small Watershed in Southeastern Ontario," Canadian Journalof Earth Sciences, 11, 893-904 (1974).

20. T. J. Wolery and J. M. Delaney, "The Reaction of Bullfrog Tuff withJ-13 Groundwater at 150'C and 90C. It. Geochemical Modeling,"Geological Society of America Abstracts with Programs, 15, 722(1983).

21. I. Neretnieks, The Movement of a Redox Front Downstream from aRepository for Nuclear Waste, KBS-TR-82-16, Royal Institute ofTechnology, Stockholm, Sweden (1982).

22. R. W. Henley, P. B. Barton, Jr., A. H. Truesdell, and J. A.Whitney, Fluid-Mineral Equilibria in Hydrothermal Systems,Reviews in Economic Geology, 1 (1984).

20

23. M. Reed and N. Spycher, 'Calculation of pH and Mineral Equilbria inHydrothermal Waters with Application to Geothermometry and Studiesof Boiling and Dilution," Geochimica et Cosmochimica Acts, 48,1479-1492 (1984).

24. D. A. Sverjensky, "Oil Field Brines as Ore-Forming Solutions,"Economic Geology, 79, 23-37 (1984).

25. H. L. Barnes, Geochemistry of Hydrothermal Ore Deposits, H. L.Barnes, ed., 2nd. ed., John Wiley & Sons, Inc., New York (1979).

26. T. 0. Early, G. K. Jacobs, and D. R. Drewes, "Geochemical Controlson Radionuclide Releases from a Nuclear Waste Repository In Basalt:Estimated Solubilities for Selected Elements," In GeochemicalBehavior of Disposed Radioactive Waste, G. S. Barney, J. D.Navratil, and W. W. Schultz, eds., American Chemical Society,Washington, D.C. (1984).

27. J. F. Kerrisk, Solubility Limits on Radionuclide Dissolution at aYucca Mountain Repository, LA-9995-MS, Los Alamos NationalLaboratory, Los Alamos, New Mexico (1984).

28. R. J. Lemire, An Assessment of the Thermodynamic Behaviour ofNeptunium in Water and Model Groundwaters from 25 to 150'C,AECL-7817, Atomic Energy of Canada Ltd., Pinawa, Manitoba,Canada (1984).

29. M. R. Schweingruber, Evaluation of Solubility and Speciation ofActinides In Natural Groundwaters, TM-45-82-11, Swiss FederalInstitute for Reactor Research, Wairenlingen, Switzerland (1982).

30. B. W. Goodwin, Maximum Total Uranium Solubility under ConditionsExpected In a Nuclear Waste Vault, AECL-TR-29, Atomic Energy ofCanada Ltd., Pinawa, Manitoba, Canada (1980).

31. T. J. Wolery, Chemical Modeling of Geologic Disposal of NuclearWaste: Progress Report and a Perspective, UCRL-52748, LawrenceLivermore National Laboratory, Livermore, California (1980).

32. E. A. Jenne, Geochemical Modeling: A Review, PNL-3574, PacificNorthwest Laboratory, Richland, Washington (1981).

33. T. 0. Early, J. Myers, and E. A. Jenne, "Applications ofGeochemical Modeling to High-Level Nuclear Waste Disposal at theHanford Site, Washington," this volume.

34. P. Ortoleva, "Modeling Water-Rock Interactions," this volume.

35. B. Grambow and De M. Strachan, "Leach Testing of Waste Glassesunder Near-Saturation Conditions," Materials Research SocietySymposium Proceedings, 26, 623-633 (1984).

36. L. N. Plummer and D. L, Parkhurst, "PHREEQE: Status andApplications," this volume.

3L0 REC0IMHENDATIONS

What are come of the key developments which could enhance the role ofgeochemical modeling In repository assessments?

As discussed in the previous section, the consensus at the conference

was that geochemical modeling will have to play a significant role In

showing that HLW can be safely isolated in deep geologic formations.

There was also a consensus that current models are inadequate to pro-

perly account for all potentially Important processes and parameters.

For geochemical modeling to progress to the point where simulations will

provide reliable predictions, significant advances will have to occur in

the areas of: (1) Applications and Processes, (2) Theory and Code

Development, (3) Thermodynamic Data, and (4) Kinetics and Coupled

Processes. Specific recommendations resulting from the conference for

these four topical areas are discussed in the following sections. No

attempt has been made to establish priorities for the recommendations,

because priorities will be somewhat dependent on the site and design

characteristics of a given repository (e.g., temperature, pressure,

ionic strength of groundwaters, hydrologic regime, etc.). In addition

to the specific technical recommendations, there is some discussion of

general recommendations which relate to the reasons for, and Implemen-

tation of, the technical recommendations. These general recommendations

are intended to Illustrate some of the problems in the current HLW

programs, and to stimulate discussion and action which might help to

promote resolution of these problems.

21

22

3.1 APPLICATIONS AND PROCESSES

Outlined below are a set of applications and processes which are

regarded crucial for Inclusion into models appropriate for predicting

the geochemical behavior of HLW repositories. Neglecting one or more

processes which could lead to conservatism may be acceptable in certain

instances, although care must be taken so as to not overlook potential

synergisms which could ultimately result in incorrect and possibly

overly optimistic estimates of performance.

(1) Transport. The transport of materials to, through, and awey from a

HLW repository is an essential component of its performance*

Geochemical mass transport models, in order to properly account for this

movement, should include (as appropriate for a particular site) the

following: (a) advection, (b) diffusion, (c) dispersion, (d) unsatu-

rated flow, (e) vapor transport, and (f) brine migration through salt.

These processes represent the major physical and chemical mechanisms

which contribute to the transport of material in most repository set-

tings, although it is obvious that all the processes are not applicable

to all the candidate rock types.

(2) Geochemical Conditions. The geochemical conditions in and around a

repository will significantly influence the containment of radionucl'des

within the waste packages and the eventual release and transport of

radionuclides away from the repository. In treating such processes,

geochemical models should account for the following parameters and

characteristics: (a) temperature, (b) pressure, (c) groundwater

chemistry, Cd) pH, (e) redox potential, and (f) solid phases pertinent

to the geologic setting and engineered materials.

23

(3) Chemical Reaction. The chemical reactions which can occur in a

repository are numerous. This complexity makes It difficult to identify

and properly account for the important reactions. A reaction should not

be neglected unless It can be shown to not affect, or to affect in a

conservative manner, the results of simulations. This determination of

conservatism should include an analysis of potential synergisms between

processes. Reactions which should be addressed Include: (a) dissolution/

precipitation [includes the behavior of waste forms, metals, packing and

backfill materials, minerals, and glass (waste form and/or rock)], (b)

aqueous speclation/complexIng, (c) sorption (physical and chemical),

and (d) colloid and particulate formation, precipitation, and filtra-

tion, etc.

(4) Radiation. To date, radiation effects have received little atten-

tion, generally because of the cost and time involved. Nevertheless,

radiation may significantly alter geochemical processes important to a

repository in ways not yet anticipated. Geochemical processes should be

coupled with important radiation effects, including: (a) radiation

damage to solids, (b) radiolysls of aqueous solutions, (c) isotopic

exchange (e.g., 14C may be an important radionuclide for some

repositories), and (d) radioactive decay. These processes have not yet

been adequately coupled with important geochemical processes and parame-

ters (e.g., redox reactions, waste form dissolution, corrosion of

metals, etc.), although radioactive decay is a mechanism commonly

Included In contaminant transport codes, and isotopic exchange has been

included in some recent geochemical-model calculations (1). Mills

and Vogt (2) and Coffman et al. (3) discuss some attempts to include

24

radionuclide inventory and radiation dose calculations Into codes

describing the behavior of waste packages. Most of the work to date on

the coupling of geochemical processes with radiation effects Is

incomplete, and much work is needed In this important area.

3.2 THEORY AND CODE DEVELOPMENT

In addition to properly describing the important processes discussed in

the previous section, there are some general and specific deficiencies

In many geochemical models which need to be addressed. Most of these

deficiencies are relevant (either directly or Indirectly) to all the

processes discussed in the previous section and need to be corrected in

order to be able to properly simulate the geochemical processes Impor-

tant to HLW Isolation.

(1) Uncertainty. Predictions of performance will be inherently uncer-

tain and the degree of uncertainty needs to be incorporated into all

analyses. There are four areas of uncertainty which should be con-

sidered: (a) Numerical uncertainty, (b) Uncertainty In analytical para-

meters, (c) Uncertainty in thermodynamic and kinetic parameters, and (d)

Documentation of uncertainty. Each of these Is discussed below.

(a) Numerical uncertainty: It is essential that the degree of

numerical uncertainty in a computer code be established and minimized to

an acceptable level as part of any code development activity. An

accounting of this numerical uncertainty must be included with the docu-

mentation for the code.

(b) Uncertainty in analytical parameters: Analytical parameters

which have associated uncertainties important to the results of mass

-

.

25

transport ca-% Listions Include: (1) chemical parameters (eog., tem-

perature, pressure, pH, redox, potential, groundvwater chemistry, proper-

ties of solid phases, etc.), (2) hydrologic parameters (e.g., porosity,

permeability, hydraulic heads, etc.), and (3) physical parameters (eog.,

thermal conductivity, stratigraphic relationships, boundary conditions,

etc.). Uncertainties In these parameters need to be carried through

calculations to determine their Impact on predicted results.

(c) Uncertainty In thermodynamic and kinetic parameters: Probably

the largest source of uncertainty In geochemical-model calculations

results from uncertainties associated with fundamental tteruodynamic and

kinetic parameters These uncertain parameters can Include: log(K)

values, entropy, heat capacity, free energy values, rate constants, and

activation energies. The choice of methods for uncertainty analyses

will depend to some extent on the type, quantity, and quality of data

available. Xethods such as simple addition of errors my be appropriate

In some cases, although care mIst be taken to properly account for

correlated errors.

(d) Documentation of uncertainty: Of equal Importance to the

actual analysis of uncertainties, is the proper documentation of the

data base (including both analytical parameters and fundamental ther-

modynamic and kinetic parameters). Documentation of a data base should

Include: the source and a short history of the value, the method of

derivation, the precision and accuracy of the value, a discussion of

Internal consistency among fundamental thermodynamic and kinetic parame-

ters, and the Identification of the most sensitive and/or uncertain

values.

26

(2) Propertiets of Solid Phases. The treatment of solid phases In most

geochemical models is inadequate in the areas of compositional effects,

surface and defect characteristics, and non-crystalline solids.

Assuming end-member, stoichiometric compositions for the calculation of

the thermodynamic free energies of solids is not appropriate for most

repository applications, where many materials will exhibit a wide range

of composition, as well as degree of crystallinity. In addition, the

presence of radiation, elevated temperatures, and other repository In-

duced effects may alter the surface and structural characteristics of

solids such that the thermodynamic properties are affected. Therefore,

to simulate repository systems which will Include assemblages of solid

phases having complex chemistry and structure, improvements in the

following areas are warranted: (a) calculation of free energies for

amorphous solid and crystalline solutions, (b) effects of radiation,

surface properties, and defect structures on the free energies of

solids, and (c) calculation of free energies for complex solids such

as glasses, zeolites, and clays.

(3) Metastability and Kinetics. It Is becoming increasingly apparent

that the assumption of complete thermodynamic equilibrium in geochemi-

cal systems is not ubiquitously valid. Metastability at both low and

high temperature among redox couples (4, 5), aqueous species, and the

formation of solids (6) can exhibit a significant influence on the

geochemical behavior of the system. Because the assumption of complete

equilibrium may not be valid for some Important geochemical processes

within a repository (erg., dissolution, precipitation, oxidation/

reduction, sorption, and speciation), it is essential that the ability

27

to account for (a) metmstability and (b) kinetic relationships be devel-

oped and incorporated into geochemical models. Further details are

discussed in the section on Kinetics and Coupled Processes.

(4) Radiolysis. Radiolysis may significantly alter some chemical

characteristics of the groundwater (e.g., pH, redox potential, and

solute speciation). During the first few hundred years of repository

history, while the waste packages are likely to remain Intact, the

effects of gacma-radlolysis will predominate over those of alpha-radioly-

8is because of the shielding by the canister of the low-energy alpha

radiation. By the time the waste packages are breached, the high energy

gamma-emitting radionuclides will be mostly decayed. Therefore, the

effects of alpha-radiolysls, although likely to be important only on a

local scale (i.e., formation of micro redox environments), will be of

potentially greater significance than those of gamma-radiolysis. Areas

related to radiolysis needing development include: (a) experimental

determination of constants necessary for radiolysis calculations (e.g.,

G-values and rate constants for reactions), (b) incorporation of

radiolysis effects into geochemical models, and (c) validation tests

of radlolysis calculations. For further information on radiolysis

effects, see (7), (8), and (9).

(5) Sorption. The use of distribution coefficients (Kd) for describing

the sorption of species during transport, though a useful measure for

relative comparisons, is not based strongly enough in a fundamental

understanding of the mechanisms Involved to allow predictions and extra-

polations of high confidence. Therefore, Improvements in two areas are

28

considered necessary: (a) better numerical treatment of sorption In

geochemical models, and (b) better experimental design of sorption

tests to obtain sound data for interpreting Important mechanisms

involved in the sorption process. For example, sorption tests uti-

lizing samples of bulk rocks crushed to an arbitrary grain size may be

inadequate for representing the actual processes and retardation effects

expected during transport in anisotropic fractured - porous media.

Predictions of migration rates for radionuclides based on this type of

data will be highly uncertain because similitude between the natural and

experimental systems is not maintained in these types of tests.

Sorption tests should be designed to produce meaningful data which can

be incorporated into fundamentally sound conceptual models appropriate

for simulating mass transport processes. Otherwise, extrapolations of

performance cannot be constrained within reasonable bounds of uncer-

tainty.

(6) Thermodynamic Data Needs. There is a critical need for basic

thermodynamic data relevant to the behavior of radionuclides in a geolo-

gic system. This subject is discussed in more detail in the section on

Thermodynamic Data. Discussions during the conference suggested that

the key elements requiring more emphasis include the actinides and tech-

netlum, although sensitivity studies may suggest others of equal

priority.

(7) Activity Coefficients for Aqueous Species. Among the con-

sideratlons In the calculation of equilibria pertinent to HLW isolation

are that aqueous solutions need to be modeled over a wide range of tonic

29

strength and temperature. In addition, information on the Ion pairs

present in solution can be essential for the meaningful interpretation

of kinetic and thermodynamic experiments. The two approaches for calcu-

latIng activity coefficients currently in use are the Pitzer-based

"specific interaction" approach (see 10, 11, 12, 13, and L4) and the

"ion association' approach, which is based on extensions of the

Debye-Huckel theory (see 13, 14, 15, and 16). Neither of the two

approaches has a clear advantage for all applications. For extrapola-

tion to high temperature and interpretation of data from kinetic experi-

ments the ion association approach provides greater utility. In

addition, further research may provide methods for extending the useful

range of the ion-pairing approach to Ionic strengths beyond 1-2 Molal.

On the other hand, the specific interaction approach can currently be

used for solutions of Ionic strengths from zero to 20 (12). Its

greatest utility is in the accurate representation of experimental data.

However, reliable extrapolations with the specific interaction approach

are difficult, especially for systems with a somewhat different bulk

chemistry. At this time, it appears that the specific-ion and Ion-

pairing approaches both have their appropriate place for a given set of

circumstances - it would seem most prudent to continue to improve and

develop information in this area utilizing both approaches.

(8) Temperature Corrections. Because of the elevated temperatures

expected in a repository system (up to 300'C), improved methods for

extrapolating thermodynamic functions to elevated temperatures must be

Incorporated into geochemical models. As a general rule of thumb

(L4), calculations at elevated temperatures can be approached through

.

30

the following assumptions: (1) a p - 0, (up to lOOC); (2) 4C

constant, (up to 200'C); and (3) aCP - f(T), (up to 3001C). As Barnes

(14) points out, data for the application of assumption (3) are not

always available. Therefore, It may be desirable to use the

"isocoulombic approach", where reactions are written such that ionic

charges cancel out. Because tons are generally the dominant contribu-

tors to Cp, this technique tends to cancel out the effects of changes In

thermodynamic properties as a function of temperature, thereby forcing

aCp toward zero and extending the useful temperature range of extrapola-

tions using assumption (t) to approximately 200'C.

(9) Pressure Corrections. Though calculations of aqueous solution

equilibria, In general, are rather Insensitive to pressure (up to 200-

300 bars), mineral-fluid and gas-fluid calculations can be significantly

affected. Therefore, to avoid unnecessary errors and to account for all

Important processes, geochemical models should incorporate a correction

for pressure. It Is Imperative, so as to avoid confusion and Inadver-

tent errors, that an explicit reference state be chosen and adhered to

rigidly.

(10) Documentation, Verification, Benchmarking, and Validation.

Geochemical models may eventually be developed to the point that they

will contain a complete and sophisticated algorithm for describing the

mass transport characteristics of a HLW repository, but for a model to

be considered reliable, there are certain additional requirements

relative to code management: (a) Documentation, (b) Verification, (c)

Benchmarkling, and (5) Validation.

31E a

(a) Documentation: Some aspects of code documentation are

discussed in Silling (17). In general, proper documentation Includes:

(1) a summary of the software, (2) a description of the conceptual,

mathematical, and numerical models, (3) a user's manual, and (4) a

discussion of code verification.

(b) Verification: This P:ocess essentially tests a model for its

mathematical correctness and Includes: (1) evaluating the algorithms

used to solve the conceptual model and its mathematical representations,

(2) comparison of results with analytical solutions to sample problems

or previously verified solutions, and (3) establishing limiting boundary

conditions and assumptions where application of the model may be

Inappropriate.

(c) Benchmarking: BUnchmarking involves making code-to-code com-

parisons using sample problems which are appropriate for the model and

its intended applications. For some geochemical models there may not be

other codes in existence similar enough to allow comparison. These

models may have to be benchmarked through sample problemb which test

only portions of the entire model.

(d) Validation: Validation Is the confirmation that a model

accurately represents the "real world." Validation can be accomplished

through comparisons with laboratory experiments or field studies (17 and

18). The use of field studies (l.e., natural analogs) for the valida-

tion of geochemical models seems most appropriate, given the long time

periods Involved In HLW isolation. In addition, however, experiments

carefully designed to test specific geochemical mechanisms can be of

32

help in attempting to validate conceptual models important to predic-

tions of mass transport (e.g., kinetic versus equilibrium control of

sorption.reactions), Krupka et al. (19) specifically discuss the vali-

dation of the thermodynamic data base for uranium in the geochemical

model WATEQ4. Further Information on validation can be found In

(20). As Plummer and Parkhurst (21) point out, validation, in addition

to obtaining key thermodynamic and kinetic data, Is one of the most cri-

tical areas to be addressed In geochemical modeling.

3.3 THERMODYNAMIC DATA

There are a great variety of thermodynamic data bases available. Many

address only geologic materials, while others include elements represen-

tatIve of radionuclides to be emplaced In HLW repositories; some are

associated with a specific geochemical model, while others are not.

This variety may appear to be advantageous in that, for a specific

application, one has the option of choosing the most appropriate data

base from among those available. However, most of the data bases con-

tain values taken from similar sources and compilations, and most of the

data bases currently in use for the assessment of HLW repositories have

not been critically evaluated. Therefore, an Informed decision to

choose among data bases is not easily accomplished - in some instances

any choice may be poor. To help resolve this situation, three recommen-

dations are offered: (a) Establish a critically evaluated compilation of

thermodynamic data, (b) Perform sensitivity studies to identify key

areas for future data development, and (c) Obtain key thermodynamic

data.

33

(1) Compilation of Thermodynamic Data: It Is essential that a criti-

cally evaluated data base be compiled. The critical evaluation must

include elements representative of the key radionuclides anticipated to

be present in HLW repositories as well as the elements Important to the

geologic sites currently being investigated. The compilation should

include: (a) uncertainties, (b) a discussion of the reliability of the

value, and (c) a short history of the source and method of determina-

tion. In addition, internal consistency must be maintained within the

data base. Otherwise, significant errors in geochemical calculations

may result (22).

(2) Sensitivity Studies: A sensitivity study evaluating the Impact

of uncertainties in thermodynamic data on the calculated results should

be undertaken concurrently, to the extent possible, with the compilation

of a critically-evaluated thermodynamic data base. In this way, key

parameters can be identified which require additional experimental

determinations to check, and/or improve, their reliability. In

addition, experimental sensitivity/scoping studies should be initiated

in order to Identify solid phases and potential aqueous complexes for

which there are no data, because the Importance of missing values cannot

be addressed through sensitivity studies unless the solid or complex is

known to exist and an estimate of the thermodynamic parameters has been

made. These scoping tests are particularly important because a large

variety of as yet unidentified aqueous complexes and solids may result

from waste/barrier/rock/water interactions in a repository.

434

(3) Data Development: Detailed recommendations on the key areas needing

immediate attention In obtaining thermodynamic data should await results

of the sensitivity analyses. However, a few general areas were iden-

tified during the conference: (a) organic complexes with radionuclides,

(b) actinide elements, (c) technetium behavior, (d) data for elevated

temperature, (e) amorphous solid and crystalline solution series, and

(f) data for clays, zeolites, glasses, etc.

3.4 KINETICS AND COUPLED PROCESSES

The development and application of kinetic and coupled-process models

pertinent to HLW isolation is still in Its infancy. It is becoming

increasingly clear, however, that such coupled-process models are

Important for adequately predicting some geochemical aspects of

performance for a repository, and should, therefore, be incorporated

Into assessment methods. During the conference, three general topics

were identified as requiring further attention: (1) Coupled Chemical

Reaction/Flow Models, (2) Sensitivity Studies, and (3) Development of

Kinetic Data.

(1) Coupled Chemical Reaction/Flow Models. Predicting the release

and transport of radionuclides from a repository located in a geologic

medium involves addressing both the geochemical and hydrologic aspects

of the system. Because of the closely related nature of geochemical

reactions and fluid flow, it is clear that to properly model the system,

the two will be have to be coupled in order to account for important

synergistic effects. Ortoleva (23) and Moore (24) point out some of the

I 35

important relationships between the chemistry and fluid flow charac-

teristics of a given system (e.g., the chemistry can influence the flow

regime, and vice versa). In coupling chemical reaction and flow, there

are two end-member bounding assumptions - equilibrium control versus

kinetic control. It Is apparent that neither approach Is completely

satisfactory for all applications, and development in both these areas

should be continued. However, for most low-temperature systems, kine-

tics is clearly the dominant factor, and efforts in both model develop-

ment and experimental studies that are directed toward evaluating the

effects of coupling kinetic relationships and mass transport need to be

intensified.

(2) Sensitivity Studies. Three areas of sensitivity analys s were

identified: (a) delineate where equilibrium vs kinetic control applies,

(b) investigate areas of 'unexpected" performance, and (c) identify

basic kinetic data needs. For any given application of coupled-process

models, one should perform sensitivity tests to determine whether a con-

ceptual model based on equilibrium control or kinetic control of geoche-

mical and mass transport processes is necessary and sufficient to

describe the behavior of the system. Repositories will go through a

thermal cycle which will influence the relative Importance of kinetic

versus equilibrium control of geochemical and mass transport processes.

For example, during the high-temperature period of repository history

(approximately the first 5) years after closure), redox reactions may

occur rapidly enough to justify the assumption of equilibrium. However,

as the temperature decreases to 50 - 130'C, these same redox reactions

may become sluggish - thus requiring a kinetic treatment. As another

36., 6

example, the formation of metastable alteration phases during the high-

temperature period may be able to be treated with thermodynamics.

However, as the temperature decreases and these phases become unstable

with respect to other more thermodynamically-favored phases, the kine-

tics of dissolution of these phases becomes important if they are con-

sidered to contribute to the retention of radionuclides released from

the waste packages. Because the selection of appropriate techniques for

simulating mass transport behavior will be somewhat dependent on whether

a particular process is at equilibrium or in a dynamic state, it Ii

Important to attempt to Identify the temperatures of transition from

kinetic to equilibrium control for the different geochemical processes

which are important to the performance of a repository (e.g., redox

equilibria, dissolution, precipitation, speciation reactions, etc.).

Sensitivity studies can also help to identify areas of 'unexpected'

behavior (23), which is crucial in attempting to reliably predict the

performance of a complex system for thousands of years. The sensitivity

analyses may also aid in identifying basic data needs for the applica-

tion of kinetics and coupled processes (24).

(3) KInetic Data. There is a paucity of basic kinetic data applicable

to repository systems. This circumstance is unfortunate because kine-

tics is likely to play a significant role in the prediction of reposi-

tory behavior. The importance of kinetics derives from the fact that

the geochemical behavior of a repository system, involving complex

waste/barrier/rock/water interactions, must be predicted as a function

of time. Therefore, kinetics, which addresses physical and chemical

changes as a function of time, must be an essential part of any

37

assessment. Experimental scoping studies are needed to Identify key

processes which require more detailed kinetic analyses. In addition,

results of sensitivity studies as discussed above may prove useful in

identifying areas needing development. The following broad categories

were identified during the conference a. needing attention: (a)

dissolution, precipitation, and growth kinetics for materials such as

minerals, glasses, metals, colloids, surface coatings, etc., (b)

kinetics of redox equilibria involving both homogenous aqueous solution

reactions and heterogenous water-rock reactions, and (c) kinetics of

speciation equilibria. One specific item which was identified as

requiring special attention is the proper characterization of effective

surface area in kinetic experiments. Rather than a bulk rock/water

ratio, it is desirable to establish the surface area/volume ratio

(25). In addition to detailed experimental and theoretical analyses,

there is also a need for 'feedback' studies addressing the potential

mediating effects of the natural chemistry of a system. For example,

minor and trace components in a groundwater may have a significant

effect on the dissolution or precipitation of phases.

3.5 GENERAL RECOMMENDATIONS

A significant number of technical recommendations have been made as a

result of the conference. It should be apparent from these recommen-

dations that there are no easy solutions to the assessment of geocheml-

cal and mass transport processes important to the performance of HLW

repositories. Improving our capability to simulate the geochemical

behavior of a HLW repository in a time-scale useful to the licensing

38

process will require significant cooperation among the current site pro-

jects as well as between DOE and NRC. Based on the technical recommen-

dations presented in previous sections, there are many areas of mutual

need in the development of models and basic data. It seems apparent

that the current site projects should cooperate more closely in iden-

tifying and developing models - and obtaining data - which would be

mutually beneficial. But first, a conceptual model should be developed

which describes all geochemIcal processes and interactions which could

potentially impact the performance of a repository from the initiation

of construction through the period of containment and isolation

(approximately 10,000 years). Such a model, which apparently has not

yet been developed and/or documented for any of the candidate sites,

could be the basis for the DOE and NRC to establish levels of detail and

understanding required to adequately describe the geochemical and mass

transport characteristics of a repository.

Throughout these proceedings there is an underlying theme that a certain

level of understanding is necessary to be able to make reliable predic-

tions and extrapolations of geochemical and mass transport processes

relevant to the performance of a repository. Although it is recognized

that the DOE site projects need to obtain basic geologic, hydrologic,

and geochemical data, the characterization of a site should also include

establishing at least a qualitative understanding of the Important pro-

cesses and mechanisms. Such an understanding will also contribute to

engineering-decision studies by allowing the impact of alternative

designs on the performance of a repository to be evaluated with some

degree of certainty.

39

Whether or not resolution of the technical recommendations will require

additional funds or simply a redistribution of emphasis and funds is not

known andIs beyond the scope of this report. It can only be strongly

recommended that technical considerations receive the necessary atten-

tion in the scheduling and funding of research, development, and testing

activities within the DOE and NRC programs. The technical community has

the right and responsibility to provide input on technical matters so

that there is an opportunity for DOE and NRC to make informed and

rational decisions. This is the primary purpose of this report - to

provide the DOE and NRC with some preliminary recommendations from the

technical community concerning the simulation of geochemical and mass

transport processes important to the performance of a RLW repository.

Implementation of these recommendations should help to ensure that the

current programs in repository development will obtain the information

necessary and sufficient to guarantee the safe disposal of nuclear

waste.

40S . .

3.6 REFERENCES

1. T. S. Bowers and H. P Taylor, "An Integrated Chemical and Stable-Isotope Model of the Origin of Mid-Ocean Ridge Hot Spring Systems,"Geological Society of America Abstracts with Programs, 16, 452(1984).

2. M. Mills and D. Vogt, "A Summary of Computer Codes for RadiologicalAssessment," NUREG/CR-3209, U.S. Nuclear Regulatory Commission,Washington, D.C. (1979).

3. W. Coffman, D. Vogt, and M. Mills, "A Summary of Computer Codes forWaste Package Performance Assessment," NUREG/CR-3669, U.S.Nuclear Regulatory Commission, Washington, D.C. (1984).

4. R. D. Lindberg and D. D. Runnells, "Ground Water Redox Reactions:An Analysis of Equilibrium State Applied to Eh Measurements andGeochemical Modeling," Science, 225, 925-927 (1984).

5. H. Ohmoto and A. C. Lasaga, "Kinetics of Reactions Between AqueousSulfates and Sulfides in Hydrothermal Systems," Geochimica etCosmochimica Acta, 46, 1727-1745 (1982).

6. W. E. Dibble, Jr. and W. A. Tiller, "Kinetic Model of ZeoliteParagenesIs in Tuffaceous Sediments," Clays and Clay Minerals,29, 323-330 (1981).

7. W. J. Gray, Gamma Radlolysis Effects on Grande Ronde BasaltGroundwater, RHO-BW-SA-315 P, Rockwell Hanford Operations,Richland, Washington (1983).

8. H. Christensen and E. Bjergbakke, Radiolysis of Groundwaters fromHLW Stored in Copper Canisters, STUDSVIK/NW-82/273, StudsvikEnergitek AB, Stockholm, Sweden (1982).

9. R. S. Glass, Effects of Radiation on the Chemical EnvironmentSurrounding Waste Canisterr In Proposed Repository Sites andPossible Effects on the Corrosion Process, SAND81-1677,Sandia National Laboratories, Albuquerque, New Mexico (1981).

10. K. S. Pitzer, "Thermodynamics of Electrolytes I: Theoretical Basisand General Equations," Journal of Physical Chemistry, 77,268-277 (1973).

11. K. S. Pitzer, "Characteristics of Very Concentrated Solutions," inChemistry and Geochemistry of Solutions at High Temperatures andPressures, D. T. Rickard and F. E. Wickman, eds., Pergamon Press,Oxford, England (1981).

41

12. C. E. Harvie and J. H. Weare, 'The Prediction of MineralSolubilities In Natural Waters: The Ra-K-Mg-Ca-Cl-SO4- 20 Systemfrom zero to High Concentration at 25Cs Geochimlca etCosmochimica Acta, 44, 981-997, (1980).

13. N. Moller, J. H. Weare, and J. Greenberg, 'Prediction of MineralSolubilities and Diagenesis In Rock/Vater Assoclaticn at High-Temperature," this volume.

14. H. L. Barnes, "Thermodynamic Problems In Speciation Modeling," thisvolume.

15. H. C. Helgeson. "Thermodynamics of Hydrothermal Systems at ElevatedTemperatures and Pressures," American Journal of Science, 267,729-804 (1969).

16. H. C. Helgeson, D. H. Kirkham, and C. C. Flowers, 'TheoreticalPrediction of the Behavior of Aqueous Electrolytes at HighPressures and Temperatures: Calculation of Activity Coefficients,Osmotic Coefficients, and Apparent Molal and Standard and RelativePartial Molal Properties to 600C and 5 kb," American Journalof Science, 281, 1249-1516 (1981).

17. S. Silling, Final Technical Position on Documentation of ComputerCodes for High-Level Waste Management, NUREG/CR-0856, U.S.Nuclear Regulatory Commission, Washington, D.C. (1983).

18. E. A. Jenne and K. M. Krupka, Validation of Geochemical Models,PNL-SA-12442. Pacific Northwest Laboratory, RIchland, Washington(1984).

19. K. M. Krupka, E. A. Jenne, and W. J. Deutsch, Validation of the'WATEQ4 Geochemical Model for Uranium, PNL-4333, Pacific NorthwestLaboratory, Richland, Washington (1983).

20. ANS, 'Guidelines for the Verification and Validation of Scientificand Engineering Computer Programs," American Nuclear Society,Draft 5 10.4 November (1981).

21. L. N. Plummer and D. L. Parkhurst, 'PHREEQE: Status andApplications," this volume.

22. J. L. Haas, Jr., 'Thermodynamic Properties of Geologic Materials:Status and Future," this volume.

23. P. Ortoleva, "Modeling Water-Rock Interactions," this volume.

24. C. H. Moore, "Flow/Reaction Models of Natural Systems", thisvolume.

25. A. C. Lasaga, 'Chemical Kinetics of Water-Rock Interactions,"Journal of Geophysical Research, 89, No. B6, 4009-4025 (1984).

a I S

CONFERENCE PROCEEDINGCS

(the extended abstracts will be Included in these sections)

4.0 SOLUTION CHEMISTRY: THEORY, CODE DEVELOPMENT, ANDNON-REPOSITORY APPLICATIONS

5.0 THERMODYNAMIC DATA

6.0 KINETICS AND COUPLED PROCESSES

7.0 APPLICATIONS OF GEOCHEMICAL MODELS

4 .

* 6 S 8.0 LIST OF PARTICIPANTS

R. D. AinesLawrence Livermore National LaboratoryP.O. Box 808, L-202Livermore, California USA 94550

M. J. AptedPacific Northwest LaboratoryP.O. Box 999Richland, Washington USA 99352

J. W. BallU.S. Geological SurveyWater Resources Division345 Middlefield Road, MS 421Menlo Park, California USA 94025

H. L. BarnesDepartment of GeosciencesThe Pennsylvania State UniversItyUniversity Park, Pennsylvania USA 16802

G. F. BirchardWaste Management BranchOffice of Nuclear Regulatory ResearchU.S. Nuclear Regulatory CommissionWashington, D.C. USA 20555

D. L. BishLos Alamos National LaboratoryMS-J978Los Alamos, New Mexico USA 87545

J. G. BlencoeOak Ridge National LaboratoryP.O. Box X, Bldg. 4500SOak Ridge, Tennessee 37831

D. S. BrownAthens Environmental Research LaboratoryU.S. Environmental Protection AgencyCollege Station RoadAthens, Georgia USA 30613

G. CederbergLos Alamos National LaboratoryP.O. Box 1663Los Alamos, New Mexico USA 87545

2

G. R. ChoppinDepartment of ChemistryFlorida State UniversityTallahassee, Florida USA 32306

1. D. ColtonIT Corporation2340 Alamo Street, S.E.Suite 306Albuquerque, New Mexico USA 87106

W. DamGeotechnical BranchOffice of Nuclear Materials

Safety and SafeguardsU.S. Nuclear Regulatory CommissionWillste BuildingWashington, D.C. USA 205S5

J. M. DelaneyLawrence Livermore National LaboratoryP.O. Box 808Livermore, California USA 94550

C. J. DuffyLos Alamos National LaboratoryMS-J514Los Alamos, New Mexico USA 87545

T. 0. EarlyRockwell Hanford OperationsP.O. Box 800Richland, Washington USA 99352

K. G. EggertLawrence Livermore National LaboratoryP.O. Box 808, L-202Livermore, California USA 94550

K. L. EricksonSandia National LaboratoryP.O. Box 5800Albuquerque, New Mexico USA 87185

J. S. FruchterPacific Northwest LaboratoryP.O. Box 999Richland, Washington USA 99352

N. C. GarlstoAtomic Energy of Canada Ltd.Whiteshell Nuclear Researcla EstablishmentPinawa, Manitoba, ROE ILO CANADA

I* a3

C. S. HaaseOak Ridge National LaboratoryP.O. Box X, Bldg. 3504Oak Ridge, Tennessee USA 37831

J. HadermannSwiss Federal Institute for

Reactor ResearchCH55303 WulrenlingenSWITZERLAND

G. R. Hel2Chemistry DepartmentUniversity of MarylandCollege Park, Maryland USA 20742

J. S. HermanDepartment of Environmental SciencesUniversity of VirginiaClark WaIlCharlottesville, Virginia USA 22903

N. HubbardBattelle Memorial InstituteOffice of Nuclear Waste Isolation505 King AvenueColumbus, Ohio USA 43201

D. IsherwoodLawrence Livermore Natiotal LaboratoryP.O. Box 808, L-204Livermore, California ESA 9&550

C. K. JacobsOak Ridge Natlonal LaboratoryP.O. Box X, Bldg. 3504Oak Ridge, Tennessee USA 37831

B. S. JensenChemistry DepartmentRiso National LaboratoryDK - 4000 RoskildeDENMARK

A. D. KelmersOak Ridge National LaboratoryP.O. Box X, Bldg. 4500SOak Ridge, Tennessee USA 37831

J. F. KerriskLos Alamos National LaboratoryP.O. Box 1663Group WX-4, .S-G787Los Alamos, New Mexico USA 87545

.~ . 4

N. C. KrotheDepartment of GeologyIndiana UniversityBloomington, Indiana USA 47401

t. M. KrupkaPacific Northwest LaboratoryP.O. Box 999Richland, Washington USA 99352

A. C. LasagaDepartment of Goology and

GeophysicsYale UniversityHew Haven, Connecticut USA 06520

S. Y. L eOak Ridge National LaboratoryP.O. Box X, Bldg. 3504Oak Ridge, Tennessee USA 37831

T. P. MalinauskasOak Ridge National LaboratoryP.O. Box X, Bldg. 4500SOak Ridge, Tennessee USA 37831

L. MayaOak Ridge National LaboratoryP.O. Box X, Bldg. 5505Oak Ridge, Tennessee USA 37831

V. McCauleyBattelle Memorial InstituteDivision of Project ManagementOffice of Nuclear Haste Isolation505 King AvenueColumbus, Ohio USA 43201

C. F. McLaneRockwell Hanford OperationsP.O. Box 800Richland, Washington USA 99352

D. MelchiorThe Earth Technology Corporation3777 Long Beach Blvd.Long Beach, California USA 90807

A. MeijerLos Alamos National LaboratoryINC-7, MS-J519P.O. Box 1663Los Alamos, New Mexico USA 87545

* ^s * 5

R. E. MeyerOak Ridge National LaboratoryP.O. Box X, Bldg. 4500NOak Ridge, Tennessee USA 37831

C. H. MooreGeochem Research Associates, Inc.400 East Third St.Bloomington, Indiana USA 47401

J. MyersRockwell Hanford OperationsP.O. Box 800Richland, Washington USA 99352

K. L. NashU.S. Geological SurveyP.O. Box 25046MS 424, Denver Federal Center.Denver, Colorado USA 80225

P. OrtolevaGeochem Research Associates, Inc.400 East Third St.Bloomington, Indiana USA 47401

V. B. ParkerDivision of Chemical ThermodynamicsNational Bureau of StandardsWashington, D.C. USA 20234

S. L. PhillipsLawrence Berkeley LaboratoryMS S0B-2239Berkeley, California USA 94720

D. J. PruettOak Ridge National LaboratoryP.O. Box X, Bldg. 4501Oak Rldge, Tennessee USA 37831

M. A. RevelliLawrence Livermore National LaboratoryP.O. Box 808, L-206Livermore, California USA 94550

J. D. RimstidtDepartment of Geological SciencesVirgina Polytechnic Institute and

State UniversityBlacksburg, Virginia USA 24060

� ab . 6

P. F. SalterRockwell Hanford OperationsP.O. Box 800Richland, Washington USA 99352

B. ScheetzMaterials Research LaboratoryThe Pennsylvania State UniversityUniversity Park, Pennsylvania USA 16802

H. R. SchweingruberSwiss Federal Institute for

Reactor ResearchCH-5303 W6urenlingenSWITZERLAND

F. G. SeeleyOak Ridge National LaboratoryP.O. Box X, Bldg. 4500SOak Ridge, Tennessee USA 37831

M. SiegelSandia National LaboratoryDivision 6431Albuquerque, New Mexico USA 87047

R. J. SilvaLawrence Berkeley LaboratoryUniversity of CaliforniaBerkeley, California USA 94720

E. D. SmithOak Ridge National LaboratoryP.O. Box X, Bldg. 1505Oak Ridge, Tennessee USA 37831

R. M. SmithRockwell Hanford OperationsP.O. Box 800Richland, Washington USA 99352

B. P. SpauldingOak Ridge National LaboratoryP.O. Box X, Bldg. 1505Oak Ridge, Tennessee USA 37831

R. J. StarmerGeotechnical BranchOffice of Nuclear Materials

Safety and SafeguardsU.S. Nuclear Regulatory CommissionWillate BldgeWashington, D.C. USA 20535

7

S. H. StowOak Ridge National LaboratoryP.O. Box X, Bldge 1505Oak Ridge, Tennessee USA 37831

D. H. StrachanBattelle Pacific Northwest LaboratoriesP.O. Box 999Battelle Blvd., PSL Bldg.Richland, Washington USA 99352

T. SullivanBrookhaven National LaboratoryBldg. 703Upton, New York USA 11973

R. W. TankDepartment of GeologyLawrence UniversityAppleton, Wisconsin USA 54911

V. S. TripathiDepartment of Applied Earth SciencesStanford UniversityStanford, California USA 94305

R. R. TurnerOak Ridge National LaboratoryP.O. 6ox X, Bldg. 1505Oak Ridge, Tennessee USA 37831

J. H. WeareDepartment of Chemistry, B-014University of California, San DiegoLa Jolla, California USA 92093

D. WesolowskiOak Ridge National LaboratoryP.O. Box X, Bldg. 4500SOak Ridge, Tennessee USA 37831

S. K. WhatleyOak Ridge National LaboratoryP.O. Box X, Bldg. 450ONOak Ridge, Tennessee USA 37831

W. B. White210 Materials Recearch LaboratoryThe Pennsylvania State UniversityUniversity Park, Pennsylvania USA 16802

I -

Ip V 1

8

T. J. WoleryLawrence Liverviore National LaboratoryUniversity of CaliforniaP.O. Box 808Livermore, California USA 94550

R. G. WymerOak Ridge National LaboratoryP.O. Box X, Bldg. 4500NOak Ridge, Tennessee USA 37831

G. T. YehOak Ridge National LaboratoryP.O. Box X, Bldg. 1505Oak Ridge, Tennessee USA 37831